The present invention is directed to DC power supplies used in human powered vehicles and, more particularly, to a controlled DC power supply for a bicycle.
Conventional electrically powered devices for human powered vehicles such as bicycles include lighting devices such as headlamps and tail lamps for night time illumination. Such devices often are powered by a dynamo (AC generator) mounted on the bicycle. In recent years, however, many conventional manually operated bicycle devices are now being controlled electrically, so the number of electric components mounted to the bicycle has risen. For example, some bicycles use electrically operated gear shifting systems and electrically operated suspension systems, and such systems employ electrical motors and control devices. Not surprisingly, the dynamos used to power the conventional electrical components frequently are used to power the additional electrical components. Since many of the additional components operate using DC voltage, the AC voltage generated by the dynamo first must be rectified into a DC voltage so that the DC voltage can be used by the components.
The voltage generated by the dynamo can fluctuate significantly depending upon the running speed of bicycle, and the voltage can fall as low as approximately 8 volts. On the other hand, many modern electrical devices require a certain minimum and stable voltage in order to operate properly. For example, in the case of a motor used to actuate a transmission element or a suspension element, when the applied voltage decreases, the motor may rotate at a speed less than the required speed, or the motor may entirely. This can cause a gear shifting mechanism to stop between gears and can cause a suspension system to stop adjusting to the riding conditions. Also, when a microcomputer is used to control the moving components, the microcomputer may operate erroneously or cease to function entirely. The problem can worsen when the power supply also is used to operate conventional bicycle lighting devices, since the voltage of the power supply often decreases when the lights are turned on.
Japanese Laid-Open Patent Publication No. 2002-262473 discloses a system that somewhat provides a stabilized voltage to a lamp. The system comprises a switching means disposed between a dynamo and the lamp, a battery charged by the dynamo, a rectifier circuit disposed between the dynamo and the battery to provide DC current to charge the battery, a voltage detector that detects a charged voltage of the battery, and a control means that switches the switching means on and off according to the detected battery voltage so that electric power is supplied intermittently to the lamp. Although such intermittent powering of the lamp causes the lamp to blink, the blinking can be made imperceptible by raising the blinking frequency. In any event, the supply of power to the lamp is limited when the detected battery voltage is below a predetermined value, thereby giving priority to charging of the battery. As a result, the system reduces the risk of improper operation of other electrical components powered by the battery.
Although the above-described system helps to reduce the risk of improperly lowering the battery voltage, it does so by turning the power supply to the lamp on and off according to the detected battery voltage. As a result, when the bicycle is operated for a long time at night, the battery still may become over-discharged, thereby reducing battery life. Additionally, since the voltage generated by the dynamo fluctuates significantly according to the speed of the bicycle, the voltage generated by the dynamo becomes high at high bicycle speeds, thereby risking overcharging of the battery and reducing the life of the battery.